214 MK. G. W. LAMPLTTGH ON THE SPEETON SEMES [May 18967, 



able to prove that the true horizon of these fossils was the upper part 

 of the Zone of Belemnites lateralis. Hence, if these ammonites were 

 sufficient to demonstrate the Portlandian age of the rocks containing 

 them, the line between Jurassic and Cretaceous in the Speeton 

 section must, I urged, be drawn at the top of this zone, as Leckenby 

 proposed, and not at its base, as Prof. Judd had suggested. 



Meanwhile the subject had been attacked from an entirely dif- 

 ferent standpoint by the Eussian geologists M. Serge Nikitin (of 

 the Russian Geological Survey) and Prof. A. Pavlow (Moscow 

 University), who had attended the meeting of the International Geo- 

 logical Congress in London in 1888, and had taken the opportunity 

 then afforded of studying the Speeton section and its fauna upon 

 the spot. These gentlemen soon afterwards published independent 

 readings of the section and its correlation, 1 differing in some im- 

 portant points, but agreeing in recognizing in the Zone of Belemnites 

 lateralis the equivalent of the ' Upper Volga Beds ' of Central 

 Russia and the Purbeck of the South of England. Nikitin however 

 considered that the ammonites afforded no evidence of the Jurassic 

 age of the beds, since they had been incorrectly determined, and 

 belonged in reality to species recognized as Neocomian in Germany. 2 

 He was thereby confirmed in his previously-expressed opinion that 

 the Upper and Lower Volga Beds of Eussia (and presumably also 

 their English equivalents) should be regarded neither as Jurassic 

 nor Cretaceous, but strictly as passage-beds between these systems. 

 Pavlow, on the other hand, thought that a stricter definition was 

 possible, especially as he regarded the Zone of Belemnites lateralis as 

 equivalent not only to the Purbeck, but also to the Portland Stone 

 of the South of England. 



In a later memoir 3 (to which I had the honour of contributing a 

 chapter respecting the stratigraphy of the deposits in the North 

 of England) Prof. Pavlow, continuing to work on the same 

 general lines, extends his study of the subject to embrace the whole 

 of the North European area, and shows that the cephalopoda of 

 these rocks confirm in most points his former conclusions. He finds 

 a certain amount of difference between the fauna of the upper and 

 the lower portions of the Zone of Belemnites lateralis, which enables 

 him to divide it into two parts characterized by different types 

 of ammonites (in the same manner as the Zone of B. jaculum is 



1 S. Nikitin, ' Quelques Excursions dans les Musees et dans les Terrains 

 Mesozoiques de 1' Europe occidental^,' Bull. Soc. Beige de Geologie, vol. iii. 

 Mem. pp. 29-58 (1889) ; A. Pavlow, ' Etudes sur le Jurassique superieur et 

 le Cretace inferieur,' Bull. Soc. Imp. Naturalistes de Moscou,' n. s. vol. iii. 

 (1889) p. 61. 



2 The German evidence becomes here of extreme importance, and I am very 

 glad to learn that the whole question is now being carefully re-studied in that 

 country. If the German equivalent of the zone of Belemnites lateralis has been 

 considered Neocomian only on the strength of the old Speeton correlation, no 

 argument could be safely deduced from this quarter. But from its geographical 

 position the succession in Germany will probably eventually be found comparable 

 with several surrounding areas, and thus the linking together of the outlying 

 regions will be more securely done than is at present possible. 



3 'Argilesde Speeton,' Moscow, 1891-1892. 



